The SIR provided K 77 SeCN (Potassium Selenocyanate); 117mg A model of the dinuclear active site found in hydrogenases has been prepared and characterized. This model consists of two Ni centers bridged by two thiolate ligands and having one terminal thiolate and one tertiary amine liganded to each Ni center (Choudhury et al. Inorg. Chem. 1994, 33, 4831-4839). In order to examine the role of selenocysteine substitution in some enzymes, we have substituted selenolates for thiolates in the model (ibid.). We wish to apply NMR and ENDOR spectroscopy to these models in anticipation of doing the same for the enzyme. These techniques will allow us to directly probe the role of the Ni selenocysteine ligand in enzyme catalysis. The proposed model studies will allow us to develop the ENDOR technique and to provide a data base with which to interpret the enzyme data. These studies require enrichment of the selenium nucleus by 77Se, the isotope of Se with a nuclear magnetic moment (I = 1/2). We will synthesize the model compound by the published procedure employing K(77SeCN) produced by the Stable Isotope Resource at LANL. Upon successful completion of the model studies, enzyme samples will be prepared by supplementing the growth medium of the bacteria involved (e.g., Desulfomicrobiurn baculaturn or Methanococcus voltae) with 77Se.